1. Field of the Invention
The present invention relates to installation of heat exchange loops (“earth loops”) for a geothermal heat pump system and to a tool for use in the installation and to a compact geothermal heat pump system.
2. The Prior Art
In recent years, heat pumps have become widely used for both heating and cooling of residential and other buildings. Because of the numerous cost and environmental advantages they provide, heat pump systems have come to replace the traditional heating/cooling systems which employ the combination of a furnace, typically gas-fired or electric, and an air-conditioning system. More specifically, as compared to gas-fired (combustion) furnaces, in a heating mode, heat pump systems provide a more uniform temperature throughout a building, without a sudden blast of hot air on start-up and do not dry out the air as do the traditional furnaces, thus maintaining a higher humidity and a healthier indoor environment. Further, because of their year round use, heat pump systems cost less per hour of use than does the combination of individual heating and cooling systems.
In geothermal heat pump systems, “earth loops” (buried in the earth) of tubing or piping substitute for the standard heat exchange coil which is used for heat exchange between the refrigerant within the coil and the exterior, ambient air and which is typically mounted outside the building. In the buried earth loop, heat exchange occurs between the refrigerant and the earth, rather than between the refrigerant and the ambient air as in a conventional heat pump system.
A significant expense unique to the geothermal heat pump systems is the cost of installation of the earth loops. Typically, a depth of approximately 3-5 feet under the surface of the earth is required for effective heat exchange between the earth loop and the earth. The earth above the 3-foot depth is more susceptible to temperature changes due to sunshine and changes in weather in general. Further, the present inventor has found that earth within 10 feet of an earth loop tube is affected by heat exchange with the earth loop, i.e. a volume of earth approximately 20 feet in diameter. Accordingly, for maximum heat exchange efficiency, earth loops should be installed with a minimum separation and at least five feet, and preferably 10 or more feet, deep in the earth.
One conventional approach to installation of earth loops involves the digging of horizontal trenches, laying the earth loops within the trenches and covering. However, this system requires removal of a considerable amount of earth and/or rock and results in disturbance of the land surface and possible damage to the landscape.
Another approach to installation of the earth loops is use of conventional well drilling equipment and a vertical orientation of the earth loops. However, this approach, in many areas of the country, is more likely to encounter bedrock and a high drilling cost. Even absent the problem of bedrock, i.e. in the coastal plain and river deltas, the earth becomes more compact with depth, resulting in higher drilling cost with increase in depth. U.S. Pat. Nos. 7,017,650, 7,270,182 and 7,431,105 are exemplary of disclosures of vertical earth loop installation.
More recently, cable pulling machinery has been adapted to earth loop installation. This technique requires both a point of entry and an exit, spaced a sufficient distance apart to provide a run of tubing or piping of a length providing sufficient heat exchange. However, the dimensions of residential property often do not provide a length of property sufficient for proper spacing between the points of entry and exit. Further, this pull-through installation necessarily uses a curved borehole which complicates filling with grout around the tubing to provide a good seal for heat exchange between the tubing and the earth.